Electron tube



Patented Oct. 27, 1936 UNITE ELECTRON TUBE Fritz Michelssen, Berlin,Germany, assgnor to Telefunken Gesellschaft fr Drahtlose Telegraphie m.b. H., Berlin, Germany, a corporation of Germany Application April 6,1934, Serial No. "719,275

In Germany August 22, *419(32 2 anims. (c1. 25o- 21tr The presentinvention relates to a method and means to focus and control an electronray pencil or beam within an electron tube of the cathode ray type.

In the prior art means adapted to concentrate or focus electron pencilsin discharge tubes have been disclosed, and at the same time a rule hasbeen indicated in reference to the depth (position) of the electronsource or issuing point inside a Wehnelt cylinder if optimum dosage (orregulation) of the volumes of electrons accessible to the anodepotential is to be preserved, even in the presence of changes of thecylinder biasing voltage. Now, for a number of practical purposes it isdesirable that the control or focusing cylinder should be given a shapeother than circular, say, the shape of an ellipse or of a polygon. Ifthe shape of the Wehnelt electrode enclosing the cathode is altered asstated, the condition regarding intervening distance of the electronsource or issue point must be chosen in such a way that the verticaldistance of the emissive point in the cathode figured in reference tothe opening surface or plane of the Wehnelt electrode turned towards theanode should not exceed the maximum radius of this electrode.

In an arrangement of the kind here concerned, one pre-supposition isthat the anode should be so shaped that the electrical fields thereofhave a chance to engage or act inside the cylinder. The said condition,for a rule respecting the intervening distance as stated, can be readilyfulfilled if the opening of the anode through which the electrons are toily is smaller than the opening of the Wehnelt electrode. If, however,the aperture of the anode is made increasingly greater, then `the sourceof the electrons must be located at greater proximity to the plane laidthrough the anterior edge of the. Wehnelt electrode, in such a way thatthe distance between the electron issue point and the said surface orplane will not be more than one-third of the maximum diameter of theWehnelt electrode if the anode aperture has become larger than the widthof the Wehnelt electrode.

To accomplish this focusing or concentrating of the electron pencil indischarge tubes arrangements in which a planar or a curved surfaceelectrode is used for the purpose of focusing electron ray beams indischarge tubes, most particularly Braun tubes used for television workhave also been proposed.

In a number of cases and purposes it is of advantage that the opening ofthe surface electrode through which the anode potential is to act shouldnot be circularly bounded, indeed, that instead of the latter` form,say, an elliptical or polygonal shape be chosen. By the aid of anelliptical form the pencil could be made for instance elongated ratherthan a punctiforxn cross-section. In an arrangement of this nature, thecondition laid down with reference to the intervening distance or spacebetween the cathode and the focusing electrode as indicated in thepresent patent specication should be fulfilled in this manner that theperpendicular distance between the emissive body and the plane laidthrough the opening of the focusing electrode should not exceed one halfof the maximum longitudinal dimension of the said opening.

While as a general rule the aperture in the anode facilitating theflight therethrough of the electrons is chosen less than the opening ofthe focusing electrode, it is in some problems and cases a prerequisiteand necessity that the anode under u no conditions should be struck bythe pencil of electron stream, while yet permitting of an efficientcontrol action upon this pencil. Hence, the width of the anode openingcould be also so enlarged that the same is equal to, or larger than, theaperture of the focusing electrode. In order that also under thesecircumstances the force lines issuing `from the anode may act as far asthe cathode, it is imperative that the source or issue point of theelectrons be placed at a greater proximity to the control electrode.Hence, the basic condition is that the vertical distance between theelectron source and a plane laid thro-ugh the aperture of the focusingelectrode should not be over one-third of the maximum opening.

For the purpose of illustrating the invention an embodiment thereof isshown in the accompanying drawing.

Referring to Figures 1 and 2, the numeral l designates a suitable glasstube forming part of a cathode ray tube, provided at its one end withthe leads 3 for the heating current, sealed at 2 into the glass tube.The electrons emitted by the cathode lament 4 are accelerated in thedirection to the anode 6. In accordance with the present invention thenumerals 5, 5 respectively, designate different types of focusing andcontrolling electrodes with a shape other than circular andaccomplishing the above mentioned conditions referring to dimensions.

With reference to Figure 1, a focusing and controlling electrode 5 ofthe shape of a polygon is illustrated. In this case the distance a ofthe electron source 4 in reference to the opening plane of the Wehneltelectrode 5 turned towards the anode 6, does not exceed one half of themaximum longitudinal dimension d of the said opening.

Another embodiment of the invention is shown in Figure 2 wherein thenumeral 5 designates a focusing and controlling electrode provided withan elliptical opening 'l with the maximum diameter d and the minimumdiameter b. Corresponding to the case illustrated in Figure 1, the'distance a of the electron source 4 in reference to the opening place ofthe electrode 5' turned towards the anode 6 does not exceed one-half ofthe maximum diameter of the opening 1.-

Having thus described the invention,-I claim:

1. An electron concentrating means for a cathode ray tube comprising across-section electro'n source, an anode, a tubularnon-cylindricalelectron beam focusing electrode surrounding the cathodeand extending beyond the same toward the anode, said focusing electrodebeing so positioned relative to the electron source that where arepresents the perpendicular distance between the source of theelectrons and the end plane of the focusing electrode adjacent the anodeand d represents the maximum diameter of the said tubularnon-cylindrical focusing electrode 2. A cathode ray tube comprising anelectron source, an anode electrode arranged in cooperative relationshipwith respect to the source so as to. cause electrons to be drawn fromthe source and to flow in an electron beam longitudinally of the tube,and a tubular non-cylindrical focusing electrode at least partiallysurrounding the electron source and extending therefrom toward theanode, the focusing electrode being so ark ranged. relative to thesource that d equals at least 2a, where d represents the maximumdiameter of the non-cylindrical tubular focusing electrode and arepresents the distance from the electron source to the end plane of thefocusing electrode adjacent the anode.

FRITZ lWICHELSSEN.

